Many pump assemblies are known for dispensing fluid including those disclosed in the applicant's U.S. Pat. No. 5,489,044 to Ophardt issued Feb. 6, 1996, the disclosure of which is incorporated herein by reference. Such fluid pumps are preferably for use with a wide variety of fluids to be dispensed which fluids have a wide variety of properties. These fluids can include alcohol and alcohol solutions, water and water based soaps and cleaners, thick creams as, for example, hand creams and facial creams and highly viscous fluids and pastes, such as toothpaste and pumice containing flowable hand cleaning compositions. These fluids have different viscosities. For example, alcohol and alcohol solutions have a low viscosity, many of the soap-like water based cleaners have a viscosity comparable to water itself whereas the thick creams may have a much higher viscosity and the extremely thick fluid or pastes, such as toothpaste, can have a very high viscosity.
The applicant has appreciated a difficulty with known disposable plastic pumps that, different pumps need to be manufactured to provide for dispensing of fluids having different properties notably different viscosities. The present applicant has appreciated that for some pumps having the same pump configuration, three different pumps are required to be manufactured with one for low viscosity solutions containing alcohol, a second for water based cleaning solutions and a third for thick creams and very viscous fluids.
In the operation of a piston pump having a flexible disk which must deflect away from a chamber wall to permit fluid to flow therepast, the viscosity of the fluid being dispensed can have a significant impact on the extent to which disk engages a wall of a chamber in which it is disposed so as on one hand to prevent flow of liquid therepast in normal operation of the pump to dispense fluid and on the other hand to permit vacuum evacuation of air therepast as in a step in a typical preparation for use of a bottle carrying the pump with at least some fluids. For example, providing engagement of a disk with a circumferential wall of a chamber so as to provide a seal against, for example, alcohol leaking thereby will also provide a seal past which it will be difficult to evacuate air using a vacuum. As a contrary example, when used for dispensing relatively thick fluid, cream or paste, there is a low tendency of the thick cream to leak past a disk on a piston engaging a cylindrical wall of a chamber and, thus, what might be considered a relatively leaky disk in the context of an alcohol fluid or water based cleaner may be an acceptable disk for use in a pump dispensing a relatively thick fluid or cream. The relatively leaky disk in the context of a relatively viscous cream can be acceptable in use of the pump for dispensing without risk of leaking of the relatively thick fluid, cream or paste and assist in permitting evacuation of air past the disk by reducing the pressures necessary to evacuate air effectively.
The present inventor has also appreciated that many piston pumps with a piston carrying a disk to seal with a cylindrical wall of a chamber with some fluids suffer the disadvantage that they can be prone to leakage when used with some fluids, particularly those of low viscosity.
The above-mentioned U.S. Pat. No. 5,489,044 teaches filling a reservoir with fluid, applying a pump assembly to the outlet of the reservoir and using a vacuum to evacuate air from the reservoir. This is advantageous for a number of reasons. Eliminating air from the reservoir can increase shelf life of the fluid as may be desired or necessary in the case of certain bio-degradable soaps, foods and pharmaceuticals. In the case of higher viscosity fluids, such as thick creams and pastes which are typically filled with the container upright, a difficulty arises when air remains in the container after filling. On inversion of the container after filling for use the fluid may have a sufficiently high viscosity that the air in the container does not rise upwardly in the container to above the fluid. Rather, the air becomes entrapped in the fluid and as the fluid is dispensed through the pump, the air becomes presented to the inlet of the pump and the air must be pumped out before further dispensing of the desired fluid resumes. A user on finding that air is being dispensed assumes that the reservoir is empty of fluid or that the pump mechanism is not working. To overcome this problem, it is particularly desired with thick fluids, creams and pastes that the container be evacuated of air before use. In order to evacuate air from the container, a vacuum can be applied to the container across a seal disk. If the seal disk is to provide a strong seal as against fluids such as alcohol or water based cleaning solutions leaking then a high vacuum below atmospheric is required to evacuate air past the disk. Thus, the present applicant has appreciated the disadvantage of a pump assembly suitable for use in dispensing alcohol is not suitable for use in dispensing thicker fluids particularly those in which air or other gases will not flow upwardly due to gravity alone. A product vendor needs to make or purchase and stock, with a disadvantage of increased cost, two different pumps.